In a Long Term Evolution (LTE) time division duplexing (TDD) system in the prior art, downlink transmission supports the hybrid automatic repeat request (HARQ) technology.
A base station transmits a PDSCH (physical downlink shared channel) or downlink semi-persistent scheduling release (SPS Release) signaling to a UE (user equipment) in a subframe n−k, and the UE transmits HARQ acknowledge (HARK-ACK) information of the PDSCH or the downlink SPS release signaling to the base station in an uplink subframe n, where k∈K, K is referred to as a downlink association set, K is a downlink association set {k0, k1, . . . , kMc−1} that includes M elements, and a downlink subframe set {n−k0, n−k1, . . . , n−kM-1} is referred to as an HARQ-ACK bundling subframe set. Specific values are shown in Table 1.
TABLE 1Downlink association setUplink-downlinkSubframe number nconfiguration01234567890——6—4——6—41——7, 64———7, 64—2——8, 7, 4, 6————8, 7, 4, 6——3——7, 6, 116, 55, 4—————4——12, 8, 7, 116, 5, 4, 7——————5——13, 12, 9, 8, 7, 5, 4, 11, 6 ———————6——775——77—
After receiving the HARQ-ACK information, the base station may learn whether the UE has correctly received the PDSCH or the downlink SPS release signaling. On the other hand, the base station transmits an uplink grant (UL Grant) to the UE in a subframe n−k′, where the UL Grant is used to indicate physical uplink shared channel (PUSCH) transmission in the uplink subframe n, where k′ is referred to as an uplink association index. Specific values are shown in Table 2.
TABLE 2Uplink association indexUplink-downlink Subframe number nconfiguration012345678916464244344444454677577
In the prior-art system, values of k′ and {k0, k1, . . . , kMc−1} and are separately defined in each uplink-downlink configuration. For any uplink-downlink configuration, a value of k′ is not greater than a value of kM-1, that is, the UL Grant is transmitted in the last subframe in the HARQ-ACK bundling subframe set, or the UL Grant is transmitted after the last subframe in the HARQ-ACK bundling subframe set. For example, when the uplink-downlink configuration is 2, the UL Grant is transmitted in a subframe 8, where the subframe 8 is the last subframe in an HARQ-ACK bundling subframe set {4, 5, 6, 8}. If the UE needs to transmit a PUSCH in the uplink subframe n, HARQ feedback information is carried on the PUSCH; otherwise, the HARQ feedback information is carried on a PUCCH (physical uplink control channel).
However, in a later release of the LTE TDD system, a base station can dynamically configure an uplink-downlink configuration, for example, it changes an uplink-downlink configuration every 10 ms to 40 ms. In this case, timing between the UL Grant and the PUSCH is determined according to an uplink reference uplink-downlink configuration, and downlink HARQ timing is determined according to a downlink reference uplink-downlink configuration, where the uplink reference uplink-downlink configuration and the downlink reference uplink-downlink configuration may be different. In this case, the UL Grant may be transmitted prior to the last subframe in the HARQ-ACK bundling subframe set.
For example, the uplink reference uplink-downlink configuration is 1, and the downlink reference uplink-downlink configuration is 2, the UL Grant is transmitted in a subframe 6, where the subframe 6 is located before the last subframe in the HARQ-ACK bundling subframe set {4, 5, 6, 8}.
It should be noted that, in the prior art, an HARQ-ACK information bit carried on a PUSCH scheduled by a UL Grant is determined according to a value of a downlink assignment index (DAI) carried by the UL Grant, where the DAI indicates the total number of PDSCHs and downlink SPS release signaling that are transmitted in the HARQ-ACK bundling subframe set. As a result, when the UL Grant is transmitted prior to the last subframe in the HARQ-ACK bundling subframe set, the DAI carried by the UL Grant may not indicate the total number of PDSCHs and downlink SPS release signaling that are transmitted in the HARQ-ACK bundling subframe set, causing the UE to feedback an incorrect HARQ-ACK information bit.
It can be easily learned that, in a case of dynamically configured uplink-downlink configuration, when a UL Grant is transmitted prior to the last subframe in an HARQ-ACK bundling subframe set, a DAI carried by the UL Grant may not indicate the total number of PDSCHs and downlink SPS release signaling that are transmitted in the HARQ-ACK bundling subframe set, thereby causing a UE to feedback incorrect HARQ-ACK information.